These years have seen the advent of the use of the chips referred to as biochips (DNA chips and the like), for the purposes of diagnosing diseases and elucidating the causes thereof, in which the probes for bio-related substances such as nucleic acids are arranged on a plane in a manner partitioned into respective different types of probes, namely, in many spots respectively immobilizing different types of probes.
For biochips, known are a method for immobilizing nucleic acids by spotting on a substrate modified chemically or physically (Science 270, 467 to 470 (1995)), and methods in which short chain nucleic acids are solid-phase synthesized directly on a silicon substrate or the like with the aid of photographic techniques (U.S. Pat. No. 5,445,934, U.S. Pat. No. 5,774,305). The spotting method suffers from a large variation from spot to spot in the amounts of the nucleic acids immobilized on the spots, so that the reproducibility from chip to chip is poor, and hence it is very difficult to produce uniform chips in quantity. The photography method is small in the variation from spot to spot in the amounts of nucleic acids immobilized on the spots and accordingly excellent in the reproducibility over a set of chips; however, the expensive manufacturing apparatus and the multistep manufacturing processes make the chips expensive, and additionally, the syntheses of nucleic acids are made on the substrate such that the syntheses of long chain nucleic acids have been difficult.
In this connection, nowadays biochips with a gel containing the immobilized probes for the bio-related substances such as nucleic acids have attracted attention which are small in the variation of the amounts of the nucleic acids immobilized on the respective spots, excellent in the reproducibility from chip to chip, independent of the nucleic acid chain lengths, and easily immobilizable to the substrate (JP Patent Publication (Kokai) No. 2000-270878, JP Patent Publication (Kokai) No. 2000-60554). In particular, the biochip disclosed in JP Patent Publication (Kokai) No. 2000-270878 is a slice obtained by cutting, along a sectional plane intersecting the fiber axis, a fiber assembly (3-dimensional array) of a plurality of hollow fibers regularly arranged and holding a bio-related substance immobilized gel which each contains a different types of bio-related substances such as a variety of nucleic acids (hereinafter referred to as a capillary array sheet). It is greatly expected in the market as an inexpensive and mass-producible biochip.
In such biochips in which probes for bio-related substances such as nucleic acids are immobilized in a gel, bio-related substance specimens such as nucleic acids in an electrolyte are made to migrate into the gel by electrophoresis, so that the probes of bio-related substances and the bio-related substance specimens are hybridized efficiently, and furthermore, the non-hybridized, unnecessary specimens can be washed out. A description of electrophoresis on the DNA chip is found in JP Patent Publication (Kokai) No. 2000-60554, which involves an electrophoretic method using a chip equipped with electrodes, and hence cannot be applied to the above described capillary array sheet. On the other hand, arranging electrodes on the chip for the purpose of conducting electrophoresis unpreferably leads to cost rising.